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Clinical History: 38-year-old man with history of back pain and ulcerative colitis. Radiographs are 5 years apart.
Findings: (A) AP radiograph from 10 years earlier demonstrates normal sacroiliac joints. Note laminectomy defect and surgical fusion at L4–5. (B) AP radiograph from 5 years earlier demonstrates bilaterally symmetric erosions of both sacroiliac joints, with surrounding sclerosis. (C) Current AP radiograph demonstrates complete ankylosis of both sacroiliac joints. Colectomy has been performed.
Differential Diagnosis: Ankylosing spondylitis, psoriatic arthritis, Reiter’s disease, rheumatoid arthritis, septic arthritis.
Diagnosis: Ankylosing spondylitis.
Discussion: Ankylosing spondylitis is a chronic inflammatory disease with predominant manifestations in the spine and sacroiliac joints. The etiology is unknown, but there is a genetic component; 90% to 95% of caucasian patients with classic ankylosing spondylitis have human leukocyte antigen (HLA-B27) (compared with 9% of all caucasians). Symptomatic disease affects about 1% of the general population; the prevalence of severe disease is about 0.1%. Therefore, the disease is much less common than rheumatoid arthritis.
Inflammatory bowel diseases associated with ankylosing spondylitis include ulcerative colitis, Crohn’s disease, and Whipple’s disease. The causal relationship of the bowel disease and the ankylosing spondylitis has not been proven definitively, but it is thought that the diseases are incidentally coexistent in some patients (those with HLA-B27), and that the spondylitis may be secondary to the bowel disease in the others (those without HLA-B27). The disease activity in the bowel does not appear to be correlated with the disease activity in the sacroiliac joints or spine.
Ankylosing spondylitis typically begins in the lumbosacral region and ascends to the cervical spine [56-57]. Local pain and tenderness over the sacroiliac joints in the early phases of the disease are common, and may dominate the initial clinical presentation. Initial involvement of the sacroiliac joints may be asymmetric or unilateral, although ultimately, bilaterally symmetric involvement is virtually invariable. Inflammatory involvement of the synovial portion of the sacroiliac joints can manifest as patchy periarticular osteoporosis, erosions of the subchondral bone leading to fraying of the osseous surface and widening of the joint space, and sclerosis of the subchondral bone. These changes predominate on the iliac side of the joint, although in advanced disease both sides are involved. Calcification and ossification of the ligamentous portion of the sacroiliac joint will accompany changes in the synovial portion of the joint. The sacroiliac joints may ultimately become blurred, sclerotic, and fused.